Large scale integrated circuit chips have many input and output connections. In order to accommodate the many connections, manufacturers have produced leadless chip carriers that use a wire bonding process. However, a wire bonding process can be expensive. In order to reduce the complexity and expense of a wire bonding process, manufacturers have increasingly used flip chip technology.
In a flip chip, an integrated circuit carries a pad arrangement on the top surface and is turned upside down (i.e., flipped), thus allowing direct coupling between the pads and matching contacts on the main circuit board or chip carrier. In a typical flip chip, solder or gold bumps are formed on the integrated circuit input/output terminals. The flip chip is directly bonded to a chip carrier or other structure by a solder connection.
U.S. Pat. No. 5,019,673 to Juskey, et al. discloses a flip chip package for integrated circuits that allows flip chip removal for ready testing and/or replacement. In the '673 patent, a flip chip package includes an over-molding of an integrated circuit assembly. A flip chip is mounted to a thin chip carrier. The flip chip includes an array of bumped pads, which fill an array of matching conductive through holes on the chip carrier. The chip carrier includes an array of bumped contacts on its back surface, which corresponds to bumped pads of the flip chip. The transfer over-molding of the integrated circuit assembly provides a layer of epoxy around the exposed surfaces of the flip chip, thus allowing an environmentally protected and removable integrated circuit package.
Although the structure does provide a removable flip chip package, processing requirements, such as microwave systems, require even greater space saving structures and manufacturing techniques that are efficient and low cost. The requirements for increased miniaturization of low volume and proprietary systems has generated a need for increased density of active devices, such as flip chips. A process for implementing flip chip packaging on a die, such as a mimic die, is not available because of grounding difficulties. This is seen especially with galium arsenide devices having an air bridge. It is also difficult to under fill these types of flip chips because of the shorting problems. Additionally, these types of chips also require grounding on the back side.